Conventional set pads oftentimes are made from foam rubber or equivalent plastic foam material. Others include liquid filling the entire pad or disposed in individual compartments. While these pads provide more comfort than a flat hard surface to a person seated thereon, there still does not result a desired type support in that the reaction of the pad is uniform over the entire surface and a seated individual tends to shift or roll from side to side or from forward to rearward positions. There is thus a certain degree of "instability".
To overcome this problem, it has been proposed to provide pads which are contoured or which are made of compositions which have a "memory". In both instances, it is usually required that the seated individual remain in the same position all the time in order to realize the best pressure distribution. In other words, the pressure points must rest within the contoured areas if the pad is to be effective.
Other type pads have incorporated a gel material or similar semi-viscous substance, but in these cases as in the case of simple foam rubber, the seating platform tends to shift and roll.
The foregoing problems are particularly acute when such pads are utilized in wheelchairs. Paraplegics are confined for great periods of time in a wheechair in a sitting position. It is vitally important to avoid skin sores and the like, and towards this end pressure distribution must be realized without introducing shear forces and without sacrificing stability.